The present invention generally relates to video display generators and more particularly to a display generator which may be employed as a graphics processor in a sonar display system, or the like, that constructs, updates and manipulates sonar images in a bit mapped memory which are displayed on a raster-type display monitor.
Acoustic display systems for use with sonar systems convert sonar data received from a sensor array into a form which is displayed on a cathode ray tube, for example. Many applications for such display systems require fast image display times and image refresh or update rates. Conventional systems which provide for rapid image display include "stroker" monitors which draw images directly on a display screen. Images which can be composed by a series of simple geometric forms are well-suited for such stroker display systems. However, the disadvantages of systems employing stroker monitors include lack of flexibility and high cost. The stroker monitor systems are also not effective when displaying complex video and graphic images. Thus, if the system requires the display of both graphic and sonar data, a second graphics display system is often needed. Furthermore, stroker monitors are baud limited, in that only so many vectors can be drawn during each refresh cycle. Accordingly, this limits the speed of conventional stroker monitors.
Raster scan displays are an inexpensive alternative to stroker displays. Raster scan displays permit an image to be built line by line, and picture element by picture element within each line. Thus, raster scan displays are capable of displaying a wide variety of image types. Furthermore, with appropriate programming, multiple images can be displayed on a single raster monitor by using viewporting, or windowing, techniques. In viewporting, different areas of a single screen are dedicated to different images. Therefore, different image types can be displayed together, or a detail of a scene may be presented with its context displayed on a smaller scale.
However, one disadvantage of conventional systems employing raster monitors is the amount of information which must be generated and formatted to characterize and build the raster image. For example, a 1K by 1K raster monitor has a million pixels. In the case of a red-green-blue (RGB) monitor of such dimensions, color and intensity information must be determined for each of these million pixels at a very fast rate to construct or update the display during each video display cycle.
In most systems using raster-type monitors, the video or acoustic information is serially written into and stored in a bit map memory, so-called because each address in the memory is mapped to a predetermined pixel on the display. Each display cycle generally involves a complete readout of the bit map memory. While the bit map memory readout can be performed rapidly, updating the bit map memory to keep pace with rapidly changing inputs from the acoustic sensor array is a problem in conventional systems due to the huge amount of information which must be generated during each display cycle. Thus, prior processors have had difficulty in updating the bit mapped memory at a rate sufficient to permit rapid readout thereof.